Genetic variability in the methylenetetrahydrofolate reductase gene (MTHFR) affects clinical expression of Wilson's disease

Ca2+ Influx through TRPC Channels Is Regulated by Homocysteine-Copper Complexes

An elevated level of circulating homocysteine (Hcy) has been regarded as an independent risk factor for cardiovascular disease; however, the clinical benefit of Hcy lowering-therapy is not satisfying. To explore potential unrevealed mechanisms, we investigated the roles of Ca²⁺ influx through TRPC channels and regulation by Hcy-copper complexes. Using primary cultured human aortic endothelial cells and HEK-293 T-REx cells with inducible TRPC gene expression, we found that Hcy increased the Ca²⁺ influx in vascular endothelial cells through the activation of TRPC4 and TRPC5. The activity of TRPC4 and TRPC5 was regulated by extracellular divalent copper (Cu²⁺) and Hcy. Hcy prevented channel activation by divalent copper, but monovalent copper (Cu⁺) had no effect on the TRPC channels. The glutamic acids (E542/E543) and the cysteine residue (C554) in the extracellular pore region of the TRPC4 channel mediated the effect of Hcy-copper complexes. The interaction of Hcy-copper significantly regulated endothelial proliferation, migration, and angiogenesis. Our results suggest that Hcy-copper complexes function as a new pair of endogenous regulators for TRPC channel activity. This finding gives a new understanding of the pathogenesis of hyperhomocysteinemia and may explain the unsatisfying clinical outcome of Hcy-lowering therapy and the potential benefit of copper-chelating therapy.

Wilson’s Disease—Genetic Puzzles with Diagnostic Implications

(1) Introduction: Wilson’s disease (WND) is an autosomal recessive disorder of copper metabolism. The WND gene is ATP7B, located on chromosome 13. WND is characterized by high clinical variability, which causes diagnostic difficulties. (2) Methods: The PubMed, Science Direct, and Wiley Online Library medical databases were reviewed using the following phrases: “Wilson’s disease”, “ATP7B genotype”, “genotype-phenotype”, “epigenetics”, “genetic modifiers”, and their combinations. Publications presenting the results of experimental and clinical studies, as well as review papers, were selected, which concerned: (i) the diversity of genetic strategies and tests used in WND diagnosis; (ii) the difficulties of genetic diagnosis, including uncertainty as to the pathogenicity of variants; (iii) genetic counseling; (iv) phenotypic effects of ATP7B variants in patients with WND and in heterozygous carriers (HzcWND); (v) genetic and epigenetics factors modifying the clinical picture of the disease. (3) Results and conclusions: The genetic diagnosis of WND is carried out using a variety of strategies and tests. Due to the large number of known variants in the ATP7B gene (>900), the usefulness of genetic tests in routine diagnostics is still relatively small and even analyses performed using the most advanced technologies, including next-generation sequencing, require additional tests, including biochemical evidence of abnormal copper metabolism, to confirm the diagnosis of WND. Pseudodominant inheritance, the presence of three various pathogenic variants in the same patient, genotypes indicating the possibility of segmental uniparental disomy, have been reported. Genotype–phenotype relationships in WND are complex. The ATP7B genotype, to some extent, determines the clinical picture of the disease, but other genetic and epigenetic modifiers are also relevant.

A Century of Progress on Wilson Disease and the Enduring Challenges of Genetics, Diagnosis, and Treatment

Wilson disease (WD) is a rare, inherited metabolic disorder manifested with varying clinical presentations including hepatic, neurological, psychiatric, and ophthalmological features, often in combination. Causative mutations in the ATP7B gene result in copper accumulation in hepatocytes and/or neurons, but clinical diagnosis remains challenging. Diagnosis is complicated by mild, non-specific presentations, mutations exerting no clear effect on protein function, and inconclusive laboratory tests, particularly regarding serum ceruloplasmin levels. As early diagnosis and effective treatment are crucial to prevent progressive damage, we report here on the establishment of a global collaboration of researchers, clinicians, and patient advocacy groups to identify and address the outstanding challenges posed by WD.

Wilson's Disease: Facing the Challenge of Diagnosing a Rare Disease

Wilson disease (WD) is a rare disorder caused by mutations in ATP7B, which leads to the defective biliary excretion of copper. The subsequent gradual accumulation of copper in different organs produces an extremely variable clinical picture, which comprises hepatic, neurological psychiatric, ophthalmological, and other disturbances. WD has a specific treatment, so that early diagnosis is crucial to avoid disease progression and its devastating consequences. The clinical diagnosis is based on the Leipzig score, which considers clinical, histological, biochemical, and genetic data. However, even patients with an initial WD diagnosis based on a high Leipzig score may harbor other conditions that mimic the WD's phenotype (Wilson-like). Many patients are diagnosed using current available methods, but others remain in an uncertain area because of bordering ceruloplasmin levels, inconclusive genetic findings and unclear phenotypes. Currently, the available biomarkers for WD are ceruloplasmin and copper in the liver or in 24 h urine, but they are not solid enough. Therefore, the characterization of biomarkers that allow us to anticipate the evolution of the disease and the monitoring of new drugs is essential to improve its diagnosis and prognosis.

COMMD1 Exemplifies the Power of Inbred Dogs to Dissect Genetic Causes of Rare Copper-Related Disorders

Wilson's Disease is a rare autosomal recessive disorder in humans, often presenting with hepatic copper overload. Finding the genetic cause of a rare disease, especially if it is related to food constituents like the trace element copper, is a Herculean task. This review describes examples of how the unique population structure of in-bred dog strains led to the discovery of a novel gene and two modifier genes involved in inherited copper toxicosis. COMMD1, after the discovery in 2002, was shown to be a highly promiscuous protein involved in copper transport, protein trafficking/degradation, regulation of virus replication, and inflammation. Mutations in the ATP7A and ATP7B proteins in Labrador retrievers and Dobermann dogs resulted in a wide variation in hepatic copper levels in these breeds. To our knowledge, numerous dog breeds with inherited copper toxicosis of unknown genetic origin exist. Therefore, the possibility that men's best friend will provide new leads in rare copper storage diseases seems realistic.

Iron metabolism is disturbed and anti-copper treatment improves but does not normalize iron metabolism in Wilson's disease

Wilson's disease (WD) is a rare hereditary disorder of copper metabolism. Some data suggest that iron metabolism is disturbed in WD and this may affect the course of the disease. The current study aimed to determine whether anti-copper treatment could affect iron metabolism in WD. One hundred thirty-eight WD patients and 102 controls were examined. Serum ceruloplasmin and copper were measured by colorimetric enzyme assay or atomic adsorption spectroscopy, respectively. Routine and non-routine parameters of iron metabolism were measured by standard laboratory methods or enzyme immunoassay, respectively. WD patients, both newly diagnosed and treated, had less serum copper and ceruloplasmin than controls (90.0, 63.0, 22.0 mg/dL, respectively, p < 0.001); in the treated patients blood copper and ceruloplasmin were lower than in untreated patients (p < 0.001). Untreated patients (n = 39) had a higher median blood iron (126.0 vs 103.5 ug/dL, p < 0.05), ferritin (158.9 vs 47.5 ng/mL, p < 0.001), hepcidin (32, 6 vs 12.1 ng/mL, p < 0.001) and sTfR (0.8 vs. 0.7 ug/mL, p < 0.001) and lower blood transferrin (2.4 vs. 2.7 g/L, p < 0.001), TIBC (303.0 vs 338.0 ug/dL, p < 0.001), hemoglobin (13.1 vs 13.9 g/dL, p < 0.01) and RBC (4.3 vs. 4.6, p < 0.002) than controls. Treated patients (n = 99) had a significantly lower median iron (88.0 vs. 126.0 ug/dL, p < 0.001), ferritin (77.0 vs. 158.9 ng/mL, p < 0.005) and hepcidin (16.7 vs. 32.6 ng/mL, p < 001) and higher transferrin (2.8 vs. 2.4 g/L, p < 0.005), TIBC (336.0 vs 303.0 ug/dL, p < 0.001), RBC (4.8 vs. 4.3 M/L, p < 0.001) and hemoglobin (14.4 vs. 13.1 g/dL, p < 0.001) than untreated; the median iron (p < 0.005) was lower, and ferritin (p < 0.005), RBC (p < 0.005) and hepcidin (p < 0.002) were higher in them than in the control group. Changes in copper metabolism are accompanied by changes in iron metabolism in WD. Anti-copper treatment improves but does not normalize iron metabolism.

Management Perspective of Wilson's Disease: Early Diagnosis and Individualized Therapy

Wilson's disease (WD) is an inherited disease caused by mutations in ATP7B and is characterized by the pathological accumulation of copper in the liver and brain. Common clinical manifestations of WD include a wide range of liver disease and neurological symptoms. In some patients, psychiatric symptoms may be the only manifestation at the time of diagnosis. The clinical features of WD are highly variable and can mimic any disease of internal medicine. Therefore, for unexplained medical diseases, the possibility of WD should not be ignored. Early diagnosis and treatment can improve the prognosis of WD patients and reduce disability and early death. Gene sequencing is becoming a valuable method to diagnose WD, and if possible, all WD patients and their siblings should be genetically sequenced. Copper chelators including D-penicillamine, trientine, and dimercaptosuccinic acid can significantly improve the liver injury and symptoms of WD patients but may have a limited effect on neurological symptoms. Zinc salts may be more appropriate for the treatment of asymptomatic patients or for the maintenance treatment of symptomatic patients. High-quality clinical trials for the drug treatment of WD are still lacking, therefore, individualized treatment options for patients are recommended. Individualized treatment can be determined based on the clinical features of the WD patients, efficacy and adverse effects of the drugs, and the experience of the physician. Liver transplantation is the only effective method to save patients with acute liver failure or with severe liver disease who fail drug treatment.

Copper Dyshomeostasis in Neurodegenerative Diseases-Therapeutic Implications

Copper is one of the most abundant basic transition metals in the human body. It takes part in oxygen metabolism, collagen synthesis, and skin pigmentation, maintaining the integrity of blood vessels, as well as in iron homeostasis, antioxidant defense, and neurotransmitter synthesis. It may also be involved in cell signaling and may participate in modulation of membrane receptor-ligand interactions, control of kinase and related phosphatase functions, as well as many cellular pathways. Its role is also important in controlling gene expression in the nucleus. In the nervous system in particular, copper is involved in myelination, and by modulating synaptic activity as well as excitotoxic cell death and signaling cascades induced by neurotrophic factors, copper is important for various neuronal functions. Current data suggest that both excess copper levels and copper deficiency can be harmful, and careful homeostatic control is important. This knowledge opens up an important new area for potential therapeutic interventions based on copper supplementation or removal in neurodegenerative diseases including Wilson’s disease (WD), Menkes disease (MD), Alzheimer’s disease (AD), Parkinson’s disease (PD), and others. However, much remains to be discovered, in particular, how to regulate copper homeostasis to prevent neurodegeneration, when to chelate copper, and when to supplement it.

Difference in iron metabolism may partly explain sex-related variability in the manifestation of Wilson's disease

BACKGROUND/AIM

Wilson's disease (WD) is a hereditary disorder characterized by abnormal metabolism of copper. For unknown reasons, the clinical picture of this disease appears to be sex-dependent. Because the metabolism of copper and iron is interrelated, we aimed to evaluate whether the variability in the clinical picture of WD could be explained by the sex difference in iron metabolism.

METHODS

A total of 138 WD patients were examined in this study: 39 newly diagnosed, treatment naive patients and 99 individuals already treated with decoppering drugs. The serum concentration of ceruloplasmin (Cp) and copper were measured using an enzymatic colorimetric assay and by atomic absorption spectroscopy, respectively. The parameters of iron metabolism were determined by using standard laboratory methods and enzyme immunoassays.

RESULTS

In the treatment naive group men had a higher median serum concentration of ferritin (290.5 vs. 81.0 ng/mL, p < 10^-4), and hepcidin (Hepc) (55.4 vs. 22.8 ng/mL, p < 10^-3) compared to women, and tended to have higher concentration of iron, hemoglobin (HGB) and number of red blood cells (RBC). In the treated group men had higher median ferritin (122.0 vs. 46.0 ng/mL, p < 10^-4), Hepc (23.5 vs. 10.8 ng/mL, p < 10^-4), iron (102.5 vs. 68.0 μg/dL, p < 10^-4), HGB (15.0 vs. 13.2 g/dL, p < 10^-4), and RBC (5.0 vs. 4.5 M/L, p < 10^-4) than women.

CONCLUSION

Iron metabolism differs between men and women with WD, which may partly explain the sex difference noted in the disease manifestation.

Effect of homeostatic iron regulator protein gene mutation on Wilson's disease clinical manifestation: original data and literature review

OBJECTIVE

Wilson's disease (WD) is a hereditary disorder of copper metabolism. The metabolic pathways of copper and iron are interrelated. Our goal was to determine the frequency of the two most common mutations in the coding region of the human iron homeostatic protein gene (HFE) in Europe: C282Y (rs1800562) and H63D (rs1799945) in WD patients, as well as to analyze their relation with WD phenotypic traits.

MATERIAL AND METHODS

HFE mutations were studied by PCR RFLP method in 445 WD patients and 102 controls. All patients met the diagnostic criteria of WD 8^th International Conference on Wilson Disease and Menkes Disease.

RESULTS

HFE C282Y heterozygotes, both women and men, showed WD symptoms earlier than patients with wild-type HFE genotype. HFE 63HD heterozygous men presented symptoms later than HFE 63HH homozygotes, but HFE 63HD women manifested symptoms later than those with HFE 63HH genotype.

CONCLUSIONS

HFE genotype seems to be one of the factors modifying Wilson's disease phenotype.

Investigation of Genetic Modifiers of Copper Toxicosis in Labrador Retrievers

Copper toxicosis is a complex genetic disorder in Labrador retrievers characterized by hepatic copper accumulation eventually leading to liver cirrhosis. The variation of hepatic copper levels in Labrador retrievers has been partly explained by mutations in ATP7A c.980C>T and ATP7B c.4358G>A. To further elucidate the genetic background of this disease, we used targeted Next Generation Sequencing (NGS) in a cohort of 95 Labrador retrievers to analyze 72 potential modifier genes for variations associated with hepatic copper levels. Variants associated with copper levels were subsequently evaluated in a replication cohort of 144 Labrador retrievers. A total of 44 variants in 25 different genes were identified, of which four showed significant association with copper levels. Of the four variants found associated with hepatic copper levels in the NGS cohort, one was validated in the replication cohort. The non-reference allele of the variant NC_006602.3.g.52434480C>T in RETN resulting in amino-acid change p.Leu7Phe was associated with decreased hepatic copper levels. In humans, resistin is associated with severity of non-alcoholic fatty liver disease, fibrosis, cirrhosis and mitochondrial dysfunction in hepatocytes. Further studies are needed to investigate the biological function of RETN p.Leu7Phe in the development of copper toxicosis in Labrador retrievers.

Dysregulated Choline, Methionine, and Aromatic Amino Acid Metabolism in Patients with Wilson Disease: Exploratory Metabolomic Profiling and Implications for Hepatic and Neurologic Phenotypes

Wilson disease (WD) is a genetic copper overload condition characterized by hepatic and neuropsychiatric symptoms with a not well-understood pathogenesis. Dysregulated methionine cycle is reported in animal models of WD, though not verified in humans. Choline is essential for lipid and methionine metabolism. Defects in neurotransmitters as acetylcholine, and biogenic amines are reported in WD; however, less is known about their circulating precursors. We aimed to study choline, methionine, aromatic amino acids, and phospholipids in serum of WD subjects. Hydrophilic interaction chromatography-quadrupole time-of-flight mass spectrometry was employed to profile serum of WD subjects categorized as hepatic, neurologic, and pre-clinical. Hepatic transcript levels of genes related to choline and methionine metabolism were verified in the Jackson Laboratory toxic milk mouse model of WD (tx-j). Compared to healthy subjects, choline, methionine, ornithine, proline, phenylalanine, tyrosine, and histidine were significantly elevated in WD, with marked alterations in phosphatidylcholines and reductions in sphingosine-1-phosphate, sphingomyelins, and acylcarnitines. In tx-j mice, choline, methionine, and phosphatidylcholine were similarly dysregulated. Elevated choline is a hallmark dysregulation in WD interconnected with alterations in methionine and phospholipid metabolism, which are relevant to hepatic steatosis. The elevated phenylalanine, tyrosine, and histidine carry implications for neurologic manifestations and are worth further investigation.

Genetics and epigenetic factors of Wilson disease

Wilson disease (WD) is a complex condition due to copper accumulation mainly in the liver and brain. The genetic base of WD is represented by pathogenic mutations of the copper-transporting gene ATP7B with consequent lack of copper excretion through the biliary tract. ATP7B is the only gene so far identified and known to be responsible for the development of the disease. Our understanding of the disease has been evolving as functional studies have associated specific disease-causing mutations with specific copper-transporter impairments. The most frequent variant in patients of European descent is the H1069Q missense mutation and it has been associated with protein misfolding, aberrant phosphorylation of the P-domain, and altered ATP binding orientation and affinity. Conversely, there is much less understanding of the relation between the genotype and the clinical manifestations of WD. WD is characterized by a highly varied and unpredictable presentation with different combined hepatic, neurological, and psychiatric symptoms. Several studies have attempted to correlate genotype and phenotype but the most recent evidences on larger populations failed to identify a relation between genotype and clinical presentations. Given that so far also modifier genes have not shown convincing association with WD, there is growing interest to identify epigenetic mechanisms of gene expression regulation as underlying the onset and progression of WD phenotype. Evidence from animal models indicated changes in methionine metabolism regulation with possible effects on DNA methylation. Mouse models of WD have indicated transcript level changes of genes related to DNA methylation in fetal and adult livers. And finally, evidence is accumulating regarding DNA methylation changes in patients with WD. It is unexplored how ATP7B genetic mutations combine with epigenetic changes to affect the phenotype. In conclusion, WD is a genetic disease with a complex regulation of its phenotype that includes molecular genetics and epigenetic mechanisms.

Whole-exome sequencing identifies novel pathogenic variants across the ATP7B gene and some modifiers of Wilson's disease phenotype

BACKGROUND & AIMS

Wilson's disease (WD) is an autosomal recessive disorder associated with disease-causing alterations across the ATP7B gene, with highly variable symptoms and age of onset. We aimed to assess whether the clinical variability of WD relates to modifier genes.

METHODS

A total of 248 WD patients were included, of whom 148 were diagnosed after age of 17. Human exome libraries were constructed using AmpliSeq technology and sequenced using the IonProton platform.

RESULTS

ATP7B p.His1069Gln mutation was present in 215 patients, with 112 homozygotes and 103 heterozygotes. Three other mutations: p.Gln1351Ter, p.Trp779Ter and c.3402delC were identified in >10 patients. Among patients, 117 had a homozygous mutation, 101 were compound heterozygotes, 27 had one heterozygous mutation, and 3 other patients had no identifiable pathogenic variant of ATP7B. Sixteen mutations were novel, found as part of a compound mutation or as a sole, homozygous mutation. For disease phenotype prediction, age at diagnosis was a deciding factor, while frameshift allelic variants of ATP7B and being male increased the odds of developing a neurological phenotype. Rare allelic variants in ESD and INO80 increased and decreased chances for the neurological phenotype, respectively, while rare variants in APOE and MBD6 decreased the chances of WD early manifestation. Compound mutations contributed to earlier age of onset.

CONCLUSIONS

In a Polish population, genetic screening for WD may help genotype for four variants (p.His1069Gln, p.Gln1351Ter, p.Trp779Ter and c.3402delC), with direct sequencing of all ATP7B amplicons as a second diagnostic step. We also identified some allelic variants that may modify a WD phenotype.

Wilson disease

Wilson disease (WD) is a potentially treatable, inherited disorder of copper metabolism that is characterized by the pathological accumulation of copper. WD is caused by mutations in ATP7B, which encodes a transmembrane copper-transporting ATPase, leading to impaired copper homeostasis and copper overload in the liver, brain and other organs. The clinical course of WD can vary in the type and severity of symptoms, but progressive liver disease is a common feature. Patients can also present with neurological disorders and psychiatric symptoms. WD is diagnosed using diagnostic algorithms that incorporate clinical symptoms and signs, measures of copper metabolism and DNA analysis of ATP7B. Available treatments include chelation therapy and zinc salts, which reverse copper overload by different mechanisms. Additionally, liver transplantation is indicated in selected cases. New agents, such as tetrathiomolybdate salts, are currently being investigated in clinical trials, and genetic therapies are being tested in animal models. With early diagnosis and treatment, the prognosis is good; however, an important issue is diagnosing patients before the onset of serious symptoms. Advances in screening for WD may therefore bring earlier diagnosis and improvements for patients with WD.

Downregulation of hepatic multi-drug resistance protein 1 (MDR1) after copper exposure

Copper homeostasis is strictly regulated in mammalian cells. We investigated the adaptation of hepatocytes after long-term copper exposure. Copper-resistant hepatoma HepG2 cell lines lacking ATP7B were generated. Growth, copper accumulation, gene expression, and transport were determined. Hepatocyte-like cells derived from a Wilson disease (WD) patient and the liver of a WD animal model were also studied. The rapidly gained copper resistance was found to be stable, as subculturing of cells in the absence of added copper (weaning) did not restore copper sensitivity. Intracellular copper levels and the expression of MT1 and HSP70 were increased, whereas the expression of CTR1 was reduced. However, the values normalized after weaning. In contrast, downregulation of multi-drug resistance protein 1 (MDR1), encoding P-glycoprotein (P-gp), was shown to be permanent. Calcein assays confirmed the downregulation of MDR1 in the resistant cell lines. MDR1 knockdown by siRNA resulted in increased copper resistance and decreased intracellular copper. Treatment of the resistant cells with verapamil, a known inducer of MDR1, was followed by increased copper-induced toxicity. Downregulation of MDR1 was also observed in hepatocyte-like cells derived from a WD patient after copper exposure. In addition, MDR1 was downregulated in Long-Evans Cinnamon rats when the liver copper was elevated. The results indicate that downregulation of MDR1 is an adaptation of hepatic cells after sustained copper exposure when ATP7B is non-functional. Our data add to the versatile functions of MDR1 in the hepatocyte and may have an impact on the treatment of copper-related diseases, prominently WD.

Nutritional Optic Neuropathy Caused by Copper Deficiency After Bariatric Surgery

A 47-year-old woman developed severe bilateral visual loss 4 years after a Roux-en-Y gastric bypass and 24 years after vertical banded gastroplasty. Her serum copper level was 35 μg/dL (normal, 80-155 μg/dL). She was prescribed elemental copper tablets. Because her methylmalonic acid was slightly elevated, she received vitamin B12 injections as well. Five weeks later, she reported that her vision had improved and, at 10 months, her vision had recovered from 20/400 bilaterally to 20/25 in each eye. This case highlights the importance of checking copper levels in addition to the "more routine" vitamin levels, such as B1, B6, B12, E, and serum folate in patients with suspected nutritional optic neuropathy after bariatric surgery, particularly if it involved a bypass procedure.

Wilson disease: At the crossroads between genetics and epigenetics-A review of the evidence

Environmental factors, including diet, exercise, stress, and toxins, profoundly impact disease phenotypes. This review examines how Wilson disease (WD), an autosomal recessive genetic disorder, is influenced by genetic and environmental inputs. WD is caused by mutations in the copper-transporter gene ATP7B, leading to the accumulation of copper in the liver and brain, resulting in hepatic, neurological, and psychiatric symptoms. These symptoms range in severity and can first appear anytime between early childhood and old age. Over 300 disease-causing mutations in ATP7B have been identified, but attempts to link genotype to the phenotypic presentation have yielded little insight, prompting investigators to identify alternative mechanisms, such as epigenetics, to explain the highly varied clinical presentation. Further, WD is accompanied by structural and functional abnormalities in mitochondria, potentially altering the production of metabolites that are required for epigenetic regulation of gene expression. Notably, environmental exposure affects the regulation of gene expression and mitochondrial function. We present the "multi-hit" hypothesis of WD progression, which posits that the initial hit is an environmental factor that affects fetal gene expression and epigenetic mechanisms and subsequent "hits" are environmental exposures that occur in the offspring after birth. These environmental hits and subsequent changes in epigenetic regulation may impact copper accumulation and ultimately WD phenotype. Lifestyle changes, including diet, increased physical activity, stress reduction, and toxin avoidance, might influence the presentation and course of WD, and therefore may serve as potential adjunctive or replacement therapies.

Currently Clinical Views on Genetics of Wilson's Disease

Objective:

The objective of this study was to review the research on clinical genetics of Wilson's disease (WD).

Data Sources:

We searched documents from PubMed and Wanfang databases both in English and Chinese up to 2014 using the keywords WD in combination with genetic, ATP7B gene, gene mutation, genotype, phenotype.

Study Selection:

Publications about the ATP7B gene and protein function associated with clinical features were selected.

Results:

Wilson's disease, also named hepatolenticular degeneration, is an autosomal recessive genetic disorder characterized by abnormal copper metabolism caused by mutations to the copper-transporting gene ATP7B. Decreased biliary copper excretion and reduced incorporation of copper into apoceruloplasmin caused by defunctionalization of ATP7B protein lead to accumulation of copper in many tissues and organs, including liver, brain, and cornea, finally resulting in liver disease and extrapyramidal symptoms. It is the most common genetic neurological disorder in the onset of adolescents, second to muscular dystrophy in China. Early diagnosis and medical therapy are of great significance for improving the prognosis of WD patients. However, diagnosis of this disease is usually difficult because of its complicated phenotypes. In the last 10 years, an increasing number of clinical studies have used molecular genetics techniques. Improved diagnosis and prediction of the progression of this disease at the molecular level will aid in the development of more individualized and effective interventions, which is a key to transition from molecular genetic research to the clinical study.

Conclusions:

Clinical genetics studies are necessary to understand the mechanism underlying WD at the molecular level from the genotype to the phenotype. Clinical genetics research benefits newly emerging medical treatments including stem cell transplantation and gene therapy for WD patients.

Canine Models for Copper Homeostasis Disorders

Copper is an essential trace nutrient metal involved in a multitude of cellular processes. Hereditary defects in copper metabolism result in disorders with a severe clinical course such as Wilson disease and Menkes disease. In Wilson disease, copper accumulation leads to liver cirrhosis and neurological impairments. A lack in genotype-phenotype correlation in Wilson disease points toward the influence of environmental factors or modifying genes. In a number of Non-Wilsonian forms of copper metabolism, the underlying genetic defects remain elusive. Several pure bred dog populations are affected with copper-associated hepatitis showing similarities to human copper metabolism disorders. Gene-mapping studies in these populations offer the opportunity to discover new genes involved in copper metabolism. Furthermore, due to the relatively large body size and long life-span of dogs they are excellent models for development of new treatment strategies. One example is the recent use of canine organoids for disease modeling and gene therapy of copper storage disease. This review addresses the opportunities offered by canine genetics for discovery of genes involved in copper metabolism disorders. Further, possibilities for the use of dogs in development of new treatment modalities for copper storage disorders, including gene repair in patient-derived hepatic organoids, are highlighted.

Wilson's disease and other neurological copper disorders

The copper metabolism disorder Wilson's disease was first defined in 1912. Wilson's disease can present with hepatic and neurological deficits, including dystonia and parkinsonism. Early-onset presentations in infancy and late-onset manifestations in adults older than 70 years of age are now well recognised. Direct genetic testing for ATP7B mutations are increasingly available to confirm the clinical diagnosis of Wilson's disease, and results from biochemical and genetic prevalence studies suggest that Wilson's disease might be much more common than previously estimated. Early diagnosis of Wilson's disease is crucial to ensure that patients can be started on adequate treatment, but uncertainty remains about the best possible choice of medication. Furthermore, Wilson's disease needs to be differentiated from other conditions that also present clinically with hepatolenticular degeneration or share biochemical abnormalities with Wilson's disease, such as reduced serum ceruloplasmin concentrations. Disordered copper metabolism is also associated with other neurological conditions, including a subtype of axonal neuropathy due to ATP7A mutations and the late-onset neurodegenerative disorders Alzheimer's disease and Parkinson's disease.

Gene variants encoding proteins involved in antioxidant defense system and the clinical expression of Wilson disease

BACKGROUND & AIMS

Wilson disease (WD) is an autosomal recessive disorder of copper metabolism resulting from pathogenic mutations of the ATP7B gene. The basis of phenotypic variability of the disease is not understood. The main mechanism of copper toxicity is probably related to generation of intracellular oxidative stress. To evaluate whether interindividual variability within genes encoding proteins involved in antioxidant defense system may modulate phenotypic expressions of WD.

METHODS

Variability within genes encoding the cytosolic enzymes: glutathione peroxidase (GPX1 rs1050450) and manganese superoxide dismutase (SOD2 rs4880), and peroxisomal enzyme: catalase (CAT rs1001179) were analysed in 435 patients. Individual genotypes were tested for their relationship with phenotypic features of WD.

RESULTS

GPX1 genotypes were not related to phenotypic manifestations of WD. Among males homozygocity for the SOD2 rs4880 T allele was related to earlier onset of WD. Patients homozygous for the CAT rs1001179 T allele characterized with later onset of WD [median (interquartile range) age: 29.0 (14.0) years vs. 22.0 (12.0) years, respectively, P < 0.004], later manifestation of hepatic symptoms [34.5 (14.0) years vs. 22.0 (12.0) years, P < 0.0009], and later presentation of neurological symptoms [37.0 (16.0) years vs. 28.0 (13.0) years, P < 0.03] than those having one or two C alleles.

CONCLUSION

Variability within the CAT gene may be an important modifier of the clinical course of WD. SOD2 genotype may influence WD phenotype among males. These observations indirectly confirm a role of oxidative stress in the pathogenesis of WD, as well as indirectly suggest that peroxisomes impairment may be involved in WD pathophysiology.

Optic neuropathy, myelopathy, anemia, and neutropenia caused by acquired copper deficiency after gastric bypass surgery

Malabsorptive bariatric surgery is rapidly becoming a major cause of copper deficiency given the increasing prevalence of these procedures for morbid obesity. Acquired copper deficiency can present with clinically significant hematologic and neurological manifestations. Although hematologic manifestations of copper deficiency are rapidly reversible, significant neurological improvement after copper supplementation therapy is unusual and many patients remain debilitated and may only experience, at best, stabilization of the neurological manifestations. Here we present a case of an undiagnosed copper deficiency several years after bariatric gastric bypass surgery, in a patient who concomitantly used zinc-containing denture cream for several years, associated with anemia, neutropenia, myelopathy, respiratory failure, and bilateral optic neuropathy, which caused major vision loss. This patient was also a heterozygote carrier of the 5,10-methylenetetrahydrofolate reductase A1298C gene polymorphism, which may affect copper metabolism. Intravenous copper repletion resulted in rapid correction of hematologic indices. However, neurological manifestations, including vision loss responded only modestly to copper supplementation, despite achieving normal blood copper concentrations. Clinicians should consider copper deficiency in patients at risk, as in this case, as a delayed diagnosis can lead to irreversible disability due to neurological manifestations.

Phenotype-genotype correlations in patients with Wilson's disease

There is considerable phenotypic variation in Wilson's disease (WD). Some patients present with hepatic disease during the first decade of life and some with neurological degeneration in adolescence or adult life, with or without overt liver disease. Although the absence of neurologic disease in patients with liver disease in childhood or adolescence can be explained by the limited time exposure of the central nervous system to copper toxicity, it is surprising that late-onset neurologic WD can occur without any evidence of liver involvement. This huge variability in the clinical presentation of WD in general reflects our limited knowledge on the natural history of WD. Genetic association studies require the phenotype to be defined as accurately as possible.

Polymorphisms of metal transporter genes DMT1 and ATP7A in Wilson's disease

Wilson's disease (WND) is an inherited disorder of copper metabolism. Divalent metal transporter1 (DMT1) and ATP7A play important roles in metal transport in humans. The frequency of two single nucleotide polymorphisms of the DMT1 gene: DMT1 IVS4 C>A, DMT1 11245 T>C and two of the ATP7A gene: rs1062472 T>C, ATP7A rs 2227291 G>C have been evaluated in a population of 108 Wilson's disease patients and 108 sex- and age-matched healthy volunteers. The DMT1 IVS4 C(+) allele occurred more frequently in WND than in the healthy controls. The allele frequencies of other studied polymorphisms in WND group were in line with frequencies obtained for healthy volunteers. Neither of the polymorphisms had an impact on the age at onset or clinical phenotype of WND.

Concordance rates of Wilson's disease phenotype among siblings

Wilson's disease (WD) is an autosomal recessive disorder characterized by the functional disruption of adenosine triphosphatase 7B (ATP7B), which results in positive copper balance. Although the primary manifestations of the disease are hepatic or neurological in scope, the factors that cause a very diverse picture of WD are not well researched. We compared the first clinical presentation, ages of onset and diagnosis, copper metabolism parameters, and ceruloplasmin levels between index cases (ICs) and their siblings. We examined 73 ICs and 95 siblings from 73 families, including a total of 168 patients with biochemical and genetically confirmed WD diagnoses. We observed an 86% concordance rate of primary clinical symptoms among ICs with hepatic symptoms and their siblings. There was 66% concordance among ICs with neurological symptoms and their siblings. No differences regarding age at onset of symptoms or copper metabolism parameters at diagnosis were identified between hepatic ICs and their siblings. The age at symptom onset did not differ between neurological ICs and their siblings, although ICs presented lower ceruloplasmin and serum copper levels. These results demonstrate a high intra-familial concordance of the clinical and biochemical presentation of WD, suggesting that similar factors shared within the same families strongly influence the disease presentation.

Influence of BDNF polymorphisms on Wilson's disease susceptibility and clinical course

Susceptibility to Wilson's disease (WD) and its clinical manifestations are thought to be affected by genetic factors, including polymorphisms. The role of brain-derived neurotrophic factor (BDNF) in the pathogenesis of neurodegenerative diseases is now widely discussed. The aim of the present study was to evaluate the frequency of the BDNF Val66Met (G-196A) and C-270T polymorphisms in WD patients and in healthy controls, and to determine the role of these polymorphisms in the clinical characteristics of WD. We found that the BDNF Val/Val (-196 G/G) and -270 C/T genotypes occurred more frequently in WD patients than in healthy controls (66 % versus 45.5 %, p = 0.0001, and 14 % versus 6 %, p = 0.018, respectively). Similarly, symptomatic patients carried the BDNF Val/Val genotype more often than presymptomatic patients (75 % versus 53 %, p = 0.0097). No association was detected between any of the determined polymorphisms and the dominant form of the disease or the age of onset for WD.

Novel ATPase Cu(2+) transporting beta polypeptide mutations in Chinese families with Wilson's disease

Wilson's disease (WD) is an autosomal recessive inherited disorder caused by mutations in the ATPase Cu(2+) transporting beta polypeptide gene (ATP7B). The detailed metabolism of copper-induced pathology in WD is still unknown. Gene mutations as well as the possible pathways involved in the ATP7B deficiency were documented. The ATP7B gene was analyzed for mutations in 18 Chinese Han families with WD by direct sequencing. Cell viability and apoptosis analysis of ATP7B small interfering RNA (siRNA)-treated human liver carcinoma (HepG2) cells were measured by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and Hoechst 33342 staining. Finally, the expression of B-cell CLL/lymphoma 2 (BCL2), BCL2-associated X protein (BAX), sterol regulatory element binding protein 1 (SREBP1), and minichromosome maintenance protein 7 (MCM7) of ATP7B siRNA-treated cells were tested by real-time polymerase chain reaction (real-time PCR) and Western blot analysis. Twenty different mutations including four novel mutations (p.Val145Phe, p.Glu388X, p.Thr498Ser and p.Gly837X) in the ATP7B gene were identified in our families. Haplotype analysis revealed that founder effects for four mutations (p.Arg778Leu, p.Pro992Leu, p.Ile1148Thr and p.Ala1295Val) existed in these families. Transfection of HepG2 cells with ATP7B siRNA resulted in decreased mRNA expression by 86.3%, 93.1% and 90.8%, and decreased protein levels by 58.5%, 85.5% and 82.1% at 24, 48 and 72 hours, respectively (All P<0.01). In vitro study revealed that the apoptotic, cell cycle and lipid metabolism pathway may be involved in the mechanism of WD. Our results revealed that the genetic cause of 18 Chinese families with WD and ATP7B deficiency-induce apoptosis may result from imbalance in cell cycle and lipid metabolism pathway.

Genetics of Wilson's disease: a clinical perspective

Hepatic Wilson's disease is often a difficult diagnosis to confirm. This review examines the current role of genetic tests for Wilson's disease and is aimed at clinicians caring for patients with this disease. We discuss how genetic testing is carried out for Wilson's disease, indications for these tests, and genetic counseling for the family. In contrast to the advances in diagnosis of Wilson's disease by testing for ATP7B mutations, genotype-phenotype correlations are not yet sufficiently established. The non-Wilsonian copper overload syndromes causing cirrhosis in children are another important area for study. The review also identifies further areas for research into the genetics of Wilson's disease in India.

Association of dopamine receptor gene polymorphisms with the clinical course of Wilson disease

BACKGROUND

Dopamine receptor D2 (DRD2) polymorphisms are proposed to be important factors in the presentation of neuropsychiatric symptoms in many disorders, including decreased striatum levels of dopamine D2 receptors in Wilson disease. The present study investigated the association between DRD2 gene polymorphisms and clinical manifestation of Wilson disease.

METHODS

Analyzing data from 97 symptomatic Wilson disease patients, we investigated the DRD2 gene polymorphisms rs1800497, rs1799732, and rs12364283. We assessed the polymorphisms impact on the phenotypic presentation of the disease.

RESULTS

Generally, the DRD2 gene polymorphisms had no impact on the hepatic or neuropsychiatric clinical presentation of Wilson disease. However, rs1799732 deletion allele carriers with neuropsychiatric symptoms had earlier onset of WD symptoms by almost 6 years compared with individuals without this allele (22.5 vs. 28.3 years; P < 0.05). This unfavorable effect of the rs1799732 polymorphism was even more pronounced among adenosine triphosphatase 7B gene (ATP7B) p.H1069Q homozygous patients, in whom carriership of the deletion allele was related to earlier initial neuropsychiatric manifestation by 14 years (18.4 vs. 32.2 years; P < 0.01).

CONCLUSIONS

Genetic variation of DRD2, specifically the rs1799732 polymorphism, may produce an earlier clinical presentation of Wilson disease neuropsychiatric symptoms and signs that occur in the course of dopaminergic system impairment due to copper accumulation in the brain. We speculate that this effect may be due to the impact of DRD2 polymorphism on dopamine D2 receptor density, but further studies are needed to understand the mechanisms of such phenotypic effects.

Evolving perspectives in Wilson disease: diagnosis, treatment and monitoring

Wilson disease (WD), the autosomal recessively inherited copper overload disorder, remains a diagnostic and therapeutic challenge. In the last decade, direct sequencing of the affected gene ATP7B became commercially available, but interpretation of the results still requires careful attention. Thus, a combination of tests reflecting the disturbed copper metabolism is needed to make the final diagnosis. Because of the low disease frequency, the existing treatment concepts are not based on controlled trails. Here, recent outcome reports of larger cohort studies challenge the recommended therapies and call for individualized treatment strategies. The notion, that certain medical regimens may either be insufficient to upkeep copper homeostasis or may lead to a clinically relevant overtreatment, demand a continuous monitoring of patients even after decades of therapy. In this article, we review current diagnostic and therapeutic approaches in WD.

Apolipoprotein E gene (APOE) genotype in Wilson's disease: impact on clinical presentation

BACKGROUND

Wilson's disease (WD), an inherited copper metabolism disorder that leads to pathological tissue copper accumulation and secondary organ damage, is caused by mutations in the ATP-ase 7B gene (ATP7B). The apolipoprotein E gene (APOE) alleles ε2, ε3, and ε4 produce three different apoE isoforms with different biological effects, which can determine risks of many human diseases, including neurodegenerative and liver disease. This study aimed to evaluate the impact of APOE genotype on the variability of WD phenotypic expression.

METHODS

We analyzed data on 383 WD consecutive patients in the WD registry. The APOE genotypes (APOE ε3/ε3 (wild-type), APOE ε2-positive, and APOE ε4-positive) were determined and the APOE genotype effect on the phenotypic WD presentation was assessed in all symptomatic WD patients, as well as in patient subgroups divided according to sex and ATP7B genotype.

RESULTS

APOE genotype had no impact on WD presentation in the general population of symptomatic patients. However, APOE ε4-positive women tended to present WD symptoms earlier than women possessing the wild-type APOE ε3/ε3 genotype (24.2 vs. 27.9 years; p = 0.08). The effect of the APOE ε4-positive genotype was more pronounced in ATP7B p.H1069Q homozygous women, in whom disease symptoms started almost 6 years earlier (23.6 vs. 29.9 years; p < 0.05) than in APOE ε3/ε3 women.

CONCLUSIONS

In women, APOE ε4-positive genotype is associated with earlier onset of WD symptoms, particularly among ATP7B p.H1069Q homozygous patients. Further studies are needed to understand the mechanisms of these gender-dependent phenotypic effects.